This invention relates generally to liquid production modulation in self-refrigerated cryogenic nitrogen gas generators; and more particularly to a method of accommodating excess refrigeration during the process of liquefying and distilling air to produce pure nitrogen.
Pure nitrogen can be obtained by liquefying and distilling air. There are many thermodynamic cycles existing for accomplishing this process. Many of them use a cryogenic expansion turbine to extract work and produce refrigeration. Frequently, the turbine produces more refrigeration than required to operate the cycle. In these cases the refrigeration is used to liquefy a portion of the purified nitrogen product and store it in a tank for use as a backup in case the plant goes off-line, or to provide extra nitrogen to handle demands above the generator output, or as source of product to be transported off-site. A problem arises when the liquid nitrogen storage tank is full and the excess refrigeration cannot be removed from the generator as liquid product. To continue operations the excess refrigeration must be disposed of in a manner which does not upset the process.
There is need for a simple method to accommodate the excess refrigeration when it is not possible or desirable to remove liquid nitrogen product.